Voltage-controlled oscillators (VCOs) within portable communication devices such as mobile telephones and other wireless devices, must exhibit low phase noise by having the largest possible signal amplitude while ensuring that devices operate within the maximum permissible voltage amplitudes. Operating the devices within voltage limits helps to increase device reliability as well as minimize the noise generated in the active devices.
Continuous-time amplitude control for voltagecontrolled oscillators has been proposed, but requires a trade-off between speed of operation and phase noise degradation resulting from low frequency bias modulation within the amplitude control loop. In addition, temperature and fabrication process variations constrain phase noise performance.
There is, therefore, a need in the art for improved amplitude control within a voltage controlled oscillator.